I can attest to this, while my pitchers are almost constantly full and they do better than the Flytraps, my Flytraps do rather well. But, their main meals seem to consist of spiders and a couple of ants, I've only seen the rare wasp or actual fly caught in the trap every once in awhile. More often than not, I see daddy long-legs' legs sticking out of the maw. It's quite neat.
As for the question, I do not know. I've never tried feeding them anything other than what they catch on their own. They'll probably be fine for quite awhile without food as long as you provide them with other adequate conditions, feeding isn't a big deal. Unless they're going to be in a food-less environment for the long haul, I think you don't have to worry about it.